This invention relates to the production of perfluorocarboxylic acids.
Perfluorocarboxylic acids are items of commerce which have a broad scope of utility. For example, perfluorooctanoic acid can be used as a reagent to provide fluorine-containing groups on a polymer molecule thus imparting water-repellency and soil-resistance to fibers and fabrics prepared from such a modified polymer. Similarly, trifluoroacetic acid can be used as a catalyst and is a chemical intermediate in the production of pharmaceutical, agricultural, and industrial products.
The production of perfluorocarboxylic acids utilizing electrochemical techniques is known and recent developments in the field of electrochemical fluorination chemistry have made such techniques even more attractive. However, the primary cell products of such electrochemical fluorination techniques are invariably in the form of the acid fluorides, e.g., trifluoroacetyl fluoride. Thus, in order to obtain the desired perfluorocarboxylic acid, e.g., trifluoroacetic acid, this primary cell product must be hydrolyzed to obtain the free acid. Such hydrolysis can be wasteful of fluorine values in that the fluorine atom of the fluoroformyl group is either lost to the process or is not readily available for recycle because it becomes dissolved in water either as HF or as a fluoride salt.
It is also known in the field of electrochemical fluorination that carboxylic acid fluorides, e.g., acetyl fluoride, are more suitable as feedstocks for electrochemical fluorination than the corresponding free acids, e.g., acetic acid, because such an electrolysis can be carried out with greater smoothness and efficiency. However, the acid fluoride forms of the carboxylic acid are more inconvenient and costly feeds in that the free acid must be converted to the acyl fluoride in a separate and preliminary step.